Moving bed contacting process

ABSTRACT

An improved moving bed contacting design is disclosed, which is especially useful for moving bed reforming. A moving catalyst bed is contained in a single, downflowing annular bed. Multiple feed inlet and outlet locations, and baffles on screens containing the catalyst, permit radial flow operation through a single bed of catalyst to simulate several distinct catalyst beds. Some gas may flow up or down, instead of radially to increase or decrease the loading of the catalyst bed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of my copending application Ser. No.625,418 filed Oct. 24, 1975, now U.S. Pat. 4,040,794, the teachings ofwhich are incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to an improved moving bed contacting process andapparatus. In one embodiment, a hydrocarbon conversion process andreactor especially useful for moving bed reforming of naphthas aredisclosed.

Description of the Prior Art

Multiple stage reaction systems for affecting the fixed-bed contactingof solids and fluids, in general, and for the fixed bed catalyticconversion of hydrocarbon streams, are well known in the art. Ingeneral, the conversion of a reactant stream over a fixed bed ofcatalyst may be conducted in upward, downward, or radial flow. Toachieve the most advantageous contact between the hydrocarbon reactantstream and catalyst particles, the catalyst is preferably disposed in anannular-form section through which the reactant stream flows laterallyand radially. Simple radial flow of reactants through a catalyst bed isshown in U.S. Pat. No. 2,683,654 (Class 23-388), the teachings of whichare incorporated by reference.

Many types of hydrocarbon conversion systems using multiple stagereactors are known. In petroleum refining technology such systems havebeen used for catalytic reforming, fixed bed alkylation, hydrorefining,hydrocracking, dehydrogenation, steam reforming, hydrogenation, etc. Thepresent invention will be described with particular reference tocatalytic reforming of naphtha, however, the inventive concept affords adistinct improvement in other hydrocarbon conversion processes as well.

Historically, catalytic reforming processes used a number ofnon-regenerative, fixed-bed reactors, usually located side-by-side. Wheninevitable catalyst deactivation occurred, one or all of the reactorswould be shutdown for catalyst regeneration, in situ. One modificationof this process was the so-called "swing-bed" system, in which four orfive reactors were provided. One reactor at a time would be regeneratedwith the other reactors remained on stream. This provided a closerapproximation of continuous operation, however, the valving required todivert very large H₂ -hydrocarbon streams around a reactor, and the needto get air into a reactor for regeneration of catalyst therein, withoutforming an explosive mixture, were serious drawbacks. Another inherentdifficulty in the swing-bed system was that every time a reactor wasplaced in service there was a "startup", which inevitably introducedminor upsets in operation.

Moving bed reaction systems are shown in U.S. Pat. No. 3,470,090 (Class208-138) and U.S. Pat. No. 3,647,680 (Class 208-65), the teachings ofwhich patents are incorporated by reference. The 3,470,090 patent showsuse of a side-by-side reaction system with intermediate heating of thereactant stream. Catalyst is withdrawn from a reaction zone and sent toregeneration facilities, then returned. In the 3,642,680 patent, astacked catalytic reforming configuration is shown. Multiple reactionzones are provided within a single large reaction vessel by providingnarrow connecting pipes between the catalyst beds. These pipes are largeenough to permit catalyst to flow by gravity, from one bed to another,but are not large enough to permit any significant amount of gas to flowfrom one reaction zone to another. Reactants are removed from onereaction zone, sent to an interheater, and charged to the next reactionzone.

The stacked reactor design of U.S. Pat. No. 3,647,680, was a significantadvance in the art of reforming of naphtha, and the process describedtherein has enjoyed world wide commercial success. With the advent ofmoving bed reforming, petroleum refiners have attempted to increase theseverity of their reforming operations. Thus, to increase yields,refiners have gone to lower pressure operation. Low pressure increasesyields, but the lowered hydrogen pressure promotes formation of coke andcarbonaceous materials on the catalyst. Similarly, there has been atrend to decrease the hydrogen to hydrocarbon mole ratio of feed to areformer to save on recycle gas compressor cost. There does not seem tobe much effect on reformate yield by merely reducing recycle gas flowrate, but reducing this flow rate does reduce the amount of energyexpended in recycling gas in the plant. Unfortunately, reduced hydrogenrecycle also promotes coke formation. Another trend has been forrefiners to opt for higher throughputs, or higher liquid hourly spacedvelocities. This requires higher temperature operation and more frequentcatalyst regeneration, but permits a refiner to make more product from agiven amount of catalyst.

All of these factors have combined to require faster turnover ofcatalyst within a reaction zone. Catalyst residence time beforeregeneration in a conventional, fixed-bed unit, is six months to severalyears. In the first moving bed reforming unit designs, catalystresidence time was about one month. The increasing demands by refinersfor higher severity operation have necessitated even more frequentregeneration, approaching complete regeneration of the entire catalystinventory of a moving bed reforming reactor in about one week.

The combination of higher space velocities, and higher catalystcirculation rates within the moving bed reactors, have lead to concernthat the existing reactor configuration may not be adequate to handlehigh catalyst flow rates. The reactor configuration of conventionalstacked reactors, such as shown in U.S. Pat. No. 3,647,680 also is verycomplex, and requires the careful assembly of a multitude of parts toinsure proper circulation of catalyst from one bed to another. Ofparticular concern is the fear that with higher LHSV's, the naphtha andhydrogen flowing laterally through the catalyst may cause some of thecatalyst to be pressed against the centerpipe of the radial flow reactorwith such force that it will not be able to flow downward smoothly. Theproblem should be most acute wherein the catalyst must move sideways toenter one of the multiple catalyst transfer points.

An improved reactor design for a fixed bed, multiple stage hydrocarbonconversion process using an annular bed of catalyst was disclosed inU.S. Pat. No. 3,751,232 (Class 23/288R), the teachings of which areincorporated by reference. In this patent, multiple reaction zones areobtained in a single reactor vessel with a single annular bed ofcatalyst. However, there is no provision for withdrawing reactants froman intermediate point in the reactor, there is only one outlet to theentire reactor. Multiple inlet points are provided, not for reactantsbut for a heat transfer medium. The patentee was trying to solve aproblem of pressure drop through the beds of catalyst, and the additionof a heat exchange medium under high pressure, via eductors, locatedbetween reaction zones was contemplated to minimize pressure dropthrough the reactor. When more than two reaction zones werecontemplated, the patentee taught that it was necessary to pierce theannular bed of catalyst with a pipe containing heat exchange medium.Placement of a large pipe laterally through a radial bed of catalystwould not hurt fluid flow in a fixed bed reactor, but in a moving bedreactor would cause poor flow of catalyst above the pipe, and form avoid space below the pipe which would permit bypassing of reactants.

One modification of the moving bed reactor scheme was disclosed in U.S.Pat. No. 3,864,240 (Class 208-64), the teachings of which areincorporated by reference. In this patent, only the terminal reactor wasa moving bed reactor, while upstream reactors were of conventional,fixed bed design, without the provision for catalyst circulation. Oneadvantage of such a reaction system is to minimize the problemsassociated with circulating catalyst from one reaction zone to the nextby gravity flow. Unfortunately, the flow scheme described in this patentdoes not provide for the continuous regeneration of the upstreamreactors, so it is not a total solution to the problem.

OBJECTS AND EMBODIMENTS

An object of the present invention is to provide an improved fluid-solidcontacting process and apparatus.

Another object is to provide an improved moving bed hydrocarbonconversion reactor and process of simplified design, with multiplereaction zones, using a single annular bed of catalyst.

Another object is to provide a moving bed reactor, with multiplereaction zones, which does not hinder flow of catalyst from one reactionzone to the next.

Accordingly, the present invention provides an apparatus for permittingfluid contact with a single vertical moving bed of catalyst particles ina plurality of reaction zones which are vertically spaced from eachother along the vertical length of the moving bed; said apparatuscomprising a vertically elongated pressure tight vessel; a pair ofvertical, concentric, inner and outer perforated screens positionedintermediate the axis of said vessel and the outer wall thereof anddefining an annular conduit which is adapted to be filled with catalystparticles defining a catalyst bed, said conduit including a plurality ofapertures at its upper and lower ends for permitting fresh catalyst tobe added to the top of said catalyst bed and spent catalyst to beremoved from the bottom, said apertures being connected to tubes whichpass through the top and bottom of said vessel; a plurality of vertical,tubular inner and outer baffle members arranged in opposed relation atspaced locations along the length of said conduit for preventing theradial flow of fluid through said catalyst bed; a plurality of inner andouter horizontal baffle members affixed to at least some of saidvertical baffle members for limiting the extent of axial flow of fluidthrough inner flow chambers defined by the hollow cylindrical spacewithin said inner perforated screen and outer flow chambers defined bythe hollow annular space between said outer perforated screen and theouter wall of the vessel, said horizontal baffles and said verticalbaffles cooperating with each other and with the wall of the vessel todivide said vessel into a plurality of separate zones; fluid inlet andoutlet means for each of said zones passing through the walls of saidvessel, the inlet means for each of said zones being connected to one ofthe inner and outer flow chambers for the zone and the outlet means foreach of said zones being connected to another of the inner and outerflow chambers for the zone, whereby at least the major portion of fluidpassing through the zone will be forced to travel radially through thecatalyst bed.

In another embodiment, the present invention provides an apparatusadapted to contain a vertical annular moving bed of catalyst andmultiple reaction zones comprising: (a) a vertically elongatedpressure-tight vessel; (b) a vertical annular catalyst bed within saidvessel and defined by a cylindrical inner perforated screen and an outerperforated screen, said screens also defining inner distributors andouter distributors; (c) a catalyst inlet means connective with the topof the catalyst bed; (d) a catalyst outlet means connective with thebottom of the catalyst bed; (e) an upper reaction zone defined at thelower limit thereof by horizontal baffles across the inner and outerdistributors, and by vertical baffles on the inner and outer screens;(f) fluid transfer means connective with the distributors within thefirst reaction zone; (g) at least one intermediate reaction zone definedby horizontal baffles across the top and bottom of the inner distributorof the reaction zone, horizontal baffles at the top, bottom and middleof the outer distributor of the reaction zone, and vertical screenbaffles at the top, bottom and middle of the reaction zone, with fluidtransfer means connective with the outer distributor above and below thehorizontal baffle in the middle of the outer distributor; (h) a lowerreaction zone defined at the upper limit thereof by horizontal bafflesacross the inner and outer distributors and vertical screen baffles;and, (i) fluid transfer means connective with the distributors withinthe last reaction zone.

In yet another embodiment, the present invention provides a process forhydrocarbon conversion of a hydrocarbon comprising contacting saidhydrocarbon at hydrocarbon conversion conditions with a single verticalmoving bed of catalyst particles disposed as a plurality of reactionzones which are vertically spaced along the vertical length of themoving bed; said zones contained in an apparatus comprising a verticallyelongated pressure tight vessel; a pair of vertical, concentric, innerand outer perforated screens positioned intermediate the axis of saidvessel and the outer wall thereof and defining an annular conduit filledwith catalyst, said conduit including a plurality of apertures at itsupper and lower ends through which apertures active catalyst is added tothe top of said catalyst bed and spent catalyst is removed from itsbottom, said apertures being connected to tubes which pass through thetop and bottom of said vessel, a plurality of vertical, tubular innerand outer baffle members arranged in opposed relation at spacedlocations along the length of said conduit for preventing the radialflow of hydrocarbon through said catalyst bed; a plurality of inner andouter horizontal baffle members affixed to at least some of saidvertical baffle members for limiting the extent of axial flow of fluidthrough inner flow chambers defined by the hollow cylindrical spacewithin said inner perforated screen and outer flow chambers defined bythe hollow annular space between said outer perforated screen and theouter wall of the vessel, said horizontal baffles and said verticalbaffles cooperating with each other and with the wall of the vessel todivide said vessel into a plurality of separate zones; fluid inlet andoutlet means for each of said zones passing through the walls of saidvessel, the inlet means for each of said zones being connected to one ofthe inner and outer flow chambers for the zone and the outlet means foreach of said zones being connected to one of the inner and outer flowchambers for the zone, whereby at least the major portion of fluidpassing through each zone will be forced to travel radially through thecatalyst bed.

In yet another embodiment, the present invention provides a process foraltering the loading exerted by a vertical moving annular bed ofparticles in a fluid stream which comprises: (a) containing in apressure tight vessel a moving bed of particles in an annular bedbetween an inner perforate screen and an outer perforate stream; (b)providing two contiguous outer annular distributors defined by the outerperforate screen, an inner wall of the pressure tight vessel, and ahorizontal, imperforate baffle intermediate the distributors; (c)providing an inner distributor defined by the inner perforate screen;(d) providing a vertical imperforate baffle, with a vertical height lessthan three times the radial thickness of the particle bed, on the innerand outer perforate screens at the same level as the horizontal,imperforate baffle; and, (e) maintaining different fluid pressures inthe outer distributors, thereby causing fluid to flow radially in fromone outer distributor through the particle bed to the inner distributor,and then to flow radially out to the other outer distributor and alsocausing verticle flow of fluid through the bed of particulates wherebythe vertical passage of fluid through the bed alters the loading exertedby the bed.

SUMMARY OF THE INVENTION

As hereinbefore stated, the present invention is applicable to movingbed fluid-solid contacting and more specifically to a multitude ofmoving bed hydrocarbon conversion processes, and especially those whichare effected in vapor phase. Illustrative of a hydrorefining process, isU.S. Pat. No. 3,696,022 (Class 208-67), the teachings of which areincorporated by reference. The operating conditions required in areforming embodiment are disclosed in the patents previously discussedand need not be mentioned in great detail. Briefly, catalytic reformingis an endothermic process effected in a plurality of reaction zones,having interstage heating facilities therebetween. Typical reformingcatalysts are spheres of one to three mm diameter. An advantage of thepresent invention is that catalyst transfer between reaction zones ismuch simplified, and it is possible to obtain good gravity flow ofcatalyst from one reaction zone to another even when the catalyst is notspherical but is instead extruded or pilled. The catalyst typicallyconsists of a Group VIII noble metal, a halogen component and a porouscarrier material, generally alumina. One or more catalyst modifiers suchas rhenium, cadmium, germanium, tin, lead, titanium, vanadium, orsulfur, etc., may be used. The operation usually occurs in vapor phaseat temperatures of 250° to 600° C. The hydrogen to hydrocarbon ratio mayrange from 0.1:1 to 20:1. The liquid hourly space velocity may rangefrom 0.2 to 20. It is anticipated that the moving bed reaction system ofthe present invention will be used at more severe conditions thanconventional fixed bed reactors, but it is of course also possible tooperate the system of the present invention at milder conventionalconditions.

Using the apparatus and process of the present invention, it is possibleto have two or many reaction zones with a single catalyst bed. Asapplied to catalytic reforming, the use of three or four zones appearsto give optimum results. Typical distribution of catalyst betweenreaction zones would be ten to 30 percent of the catalyst in a firstzone, 20 to 40 percent in a second zone, and 40 to 60 percent in a thirdzone. The precise distribution of catalyst between zones depend on thenature of the charge stock, product desired, and processing conditions.In general, for charge stocks containing very high naphtha content, moreof the catalyst should be shifted to the latter zones.

The present invention can be best understood by comparing it to anddifferentiating it from a conventional stacked reactor moving bedsystem. In a conventional stacked reactor design, the gas flow isidentical to the gas flow experienced in a conventional side-by-sidefixed bed reformer operating with radial flow. Gas enters the top of thereactor chamber, flows to an outer, annular chamber encompassing thecatalyst bed, and flows radially in through the catalyst bed, iscollected in a centerpipe and withdrawn from the reaction vessel via thecenterpipe. This gas flow is repeated throughout each reaction zone.Catalyst enters each reaction zone via multiple, spaced apart catalystaddition points, and is withdrawn in the same fashion. Regardless of thenumber of catalyst addition and withdrawal points, there must always besome lateral flow of catalyst before it can enter a catalyst withdrawalpipe. There is always the possibility of catalyst "bridging" or failingto flow properly. Catalyst must pass through lengths of pipe from thebottom of a bed to the top of reactor bed in the next section. Thecatalyst then must flow laterally to fill the bed of catalyst andprevent void spaces. The opening through which catalyst must pass is sosmall that it may be compared to the opening in an hour glass. Thus, inthe conventional stacked reactor design, gas flow is conventional, withradically different catalyst flow.

In contrast, in the reactor design of the present invention, thecatalyst is free to move, without obstruction, from the top of thereactor chamber to the bottom. There still must be catalyst addition atthe top of the reactor, and catalyst withdrawal at the very bottom ofthe reactor, but eliminated are the multiple catalyst injection andwithdrawal points required between zones in the prior art design. It ispossible to obtain several reaction zones with a unitary catalyst bed bybaffling the outer annular vapor space to broadly define each reactionzone. These baffles will prevent gas from merely bypassing the reactionzone in downward flow. The gas is forced to pass through laterallyacross the catalyst bed rather than vertically down through thecatalyst, because there is less pressure drop for the gas to flowlaterally through the relatively thin bed of catalyst encountered inthat direction, rather than horizontally downward. Once gas enters thecenterpipe, it is blocked from further passage down through thecenterpipe by baffles located in the centerpipe, so the gas takes thepath of least resistance, in this case, it flows laterally out throughthe catalyst bed.

Thus, fluid can be added to and removed from an intermediate zone of thereactor vessel by piercing the outer wall of the vessel to admit gasinto the outer radial area encompassing the catalyst bed, and byproviding a complementary withdrawal point, and an intermediate bafflebetween the fluid inlet and outlet, which will withdraw gas from theannular space around that reaction zone. In the top and bottom reactionzones, it is possible to use one-half of the conventional gascirculation scheme. As applied to the top portion of the reactor, thismeans gas may enter the centerpipe of the top reactor and flow radiallyin to out and be withdrawn from the outer annular space. Similarly, forthe last reaction zone, it would be possible to charge reactants to theouter annular space encompassing the lowermost bed of catalyst, andwithdraw catalyst from the centerpipe of the last reaction zone.Accordingly, catalyst flows simply in the present invention, while thegas flow path is complex.

It is not necessary to operate in this semi-conventional fashion oneither the first or last reaction zone, but is preferred to do so asgetting gas in and out of the reaction zones is simplified. Operationwith gas flowing as it does in an intermediate zone, i.e., radial in,followed by radial out, is also acceptable.

It is preferred that the points of gas entry and discharge be multiplepoints rather than single points. Especially preferred are multipleinjection and withdrawal points with symmetrical piping to promoteuniform gas flow through all parts of the catalyst. In general, thethicker the catalyst bed, and the higher the pressure drop across thecatalyst bed, the less critical will be multiple, symmetrically spacedinjection points. High pressure drop may be caused by a thick bed ofcatalyst, or by partially plugged screens. Screens with the percent openarea varying with vertical spacing may also be used. Because of themultiple reaction zones contemplated for use in the present invention,and because of the excellent mixing of fluid streams which occursthrough each stage of interheating, any maldistribution of fluid flowthrough the catalyst does not have a catastrophic effect, but merelyslightly reduces the efficiency of catalyst contact or reheating ofreactants.

Catalyst flow must be downward, by gravity. It is preferred, though notessential, that the reaction zones progress serially down through thereaction vessel, with the first reaction zone being uppermost and thelast reaction zone being at the bottom. Such a gas flow is preferredbecause it turns one of the "defects" of this design into a virtue. Thedefect is gas bypassing from one reaction zone to the next zone viavertical downflow of gas through the reaction bed. Any such bypassingwhich occurs will actually promote flow of catalyst down the bed. Thisis in contrast to the conventional stacked reactor design wherein flowof gas downward through the catalyst transfer pipes is so minuscle as tobe of little benefit in moving catalyst.

Depending upon the amount of catalyst boosting desired, and dependingupon the amount of bypassing of the catalyst bed which can be tolerated,the thickness of the baffles between catalyst beds can vary from merelya point thickness to a thickness equivalent to three or four times thethickness of the annular bed. There will be maximum by-passing of gasaround a reaction zone, and maximum boosting or thrusting action on thecatalyst, when baffles in the annular space or in the centerpipe arevery thin. When the baffles are twice as thick as the catalyst bed, gasflow will be roughly proportional to cross-sectional surface areaavailable for flow. Gas will have to travel just as far to pass radialin and radial out, i.e., two times across the bed, as it will have totravel in bypassing the reactor by passing down through the bed ofcatalyst from one zone to the next. Since the gas path is about the samedistance in each instance, i.e., the length of the path which eachmolecule of gas must travel, is two times the thickness of the catalystbed, the gas flow will be proportional to surface area. Thus, for areactor with a center pipe radius of one meter, and the radius of acircle enclosing the outermost limits of the catalyst bed being twometers, the cross-sectional area of the catalyst bed is about 9.4 m².For an intermediate reaction zone, seven meters high, with verticalscreen baffles two m high, the average area exposed to radial flow isabout 66.0 m² so one-eighth of the gas would bypass, i.e., not pass inradial flow, but pass via downflow, while seven-eighths of the gas wouldpass in radial flow. Increasing the length of the impervious screenbaffles from 2X to 3X the bed thickness will reduce by two-thirds theone-eighth bypassing to one-twelfth bypassing. Even here the amount ofbypassing is not critical, in that the reactants still contact thecatalyst. In a sense the only bypassing that occurs is bypassing of theinterheaters, so that the reactants must be heated to a slightly highertemperature so that the desired temperature will be achieved in thereactor when gas that has passed through the interheater contacts and ismixed with gas that has bypassed the interheater in the next reactionstage. As the total temperature drop typically encountered in a multibedreforming reactor is only about 120° C. and because eleven-twelfths ofthe fluid would pass through the interheaters, the increase ininterheater duty is one-twelfth of 120° C., or 10° C., which translatesinto an average increase in the outlet temperature of each heater ofabout 3° C., for a three zone system, which is a tolerable price to payfor the other benefits obtained through the practice of the presentinvention. Another interesting feature of the present invention is thatthere is no stagnant catalyst between beds. All prior art reactorsknown, both fixed bed and moving bed, must allow for some space at thetop and bottom of a reaction zone for catalyst distribution andwithdrawal. This reactor suffers the same infirmities as prior artreactors, but only at the top and very bottom of the annular bed ofcatalyst. Catalyst between zones still contacts reactants, viabypassing. There is no wasted or stagnant catalyst between reactors 1and reactor 2, and between reactor 2 and reactor 3. All of the catalystmay be used all of the time if a lot of bypassing can be tolerated. Thisis in contrast to conventional designs wherein 2 to 5% of the catalystvolume is in areas where it never is in the main stream of reactantflow.

Another advantage of the reactor design of the present invention is thatit permits shifting of relative catalyst distributions in the reactionzones without great difficulty. Thus, if the source of feedstock for areformer changes, e.g., from an Arabian to a Venezuelan derived naphtha,and there is a significant change in the naphthene content of feed,optimum reactor design calls for a shift in catalyst distribution. Thus,in a three zone reformer, a refiner may find it desirable to go from a20-30-50 catalyst distribution through his three reforming zones to amore skewed distribution, e.g., 10-40-50. Such a change would beimpossible in conventional fixed bed, side-by-side reforming reactorsbecause an existing reactor cannot be expanded to contain more catalyst,at least not expanded enough to accommodate a 33% increase in catalystloading such as would be experienced by the second reactor. It wouldalso be very difficult to change catalyst distribution in a conventionalstacked reactor system, because of the size and complexity of thestacked reactors, and because very large diameter pipes pass through thereaction vessel and under a reaction zone to remove fluids from thecenterpipe of intermediate reaction zones. Such modification isextremely difficult. In contrast, in the reactor design of the presentinvention it would be possible to shift the catalyst loading by raisingor lowering the screen baffles and horizontal baffles in thedistributors. Since, in some embodiments, the screens containing theannular bed of catalyst are perfectly cylindrical throughout the entirelength of the reactor, there would be no insurmountable problemencountered in merely raising or lowering the baffles. Of course, it maybe necessary to provide multiple, vertically spaced, fastening means forattaching horizontal and vertical baffles to screens and in distributorsif such operating flexibility is desired. It will also be necessary toprovide at least enough space in the centerpipe and in the outerdistributor so that a workman can enter the space and shift the locationof the screens, and re-seal the baffles to the reactor walls withasbestos rope or other sealing material. Alternatively, it should bepossible, though much more expensive, to provide for floating internalswhich could be raised or lowered by operation of a cable. Floatinginternals, i.e., vertically movable during operations, would requiremuch closer fit between the screens and the vessel walls to provideadequate sealing, so such flexible operation is not believed necessaryfor most units.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a simplified flow diagram, not to scale, illustrating anapparatus and process especially useful to moving bed reforming.

DETAILED DESCRIPTION

Reactor 1 consists of a containment vessel 3 having reactant inlet 2. Inthe reforming embodiment, hot hydrogen and fresh feed, a naphtha, entervia inlet 2 fluid distributing space 4 defined by the inner walls ofcatalyst containment screen 5. Reactants pass through screen 5 into thecatalyst maintained as a moving bed 6, and through outer screen 7 toenter outer annular space 8. Gas flow downward through the reactor isblocked in inner distributing space 4 by partition 10, and in outerannular space 8 by partition 9. Over 90% of the gas entering via inlet 2is removed via outlet 11 and charged to a heater 60.

The uppermost section of reactor 1 is designated zone 1. Zone 1 isequivalent to the first reactor in a conventional reformer. The top ofzone number 1 is defined by the lower edge of impervious baffle 12. Thelower boundary of zone 1 is defined by the lower edge of baffle 13. Theentire amount of catalyst in zone 1 is active because it sees reactantsall of the time. There is some bypassing of reactants from zone 1 tozone 2, via the catalyst bed rather than via interheater 60, but gasbypassing the heater does not bypass the catalyst. To promote maximumheater efficiency, the reactor should be designed to preferably limitbypassing to no more than 10%.

Reheated reactants leave heater 60 and enter zone 2 via line 14. Hotgases enter annular distributing space 15 and pass through screen 7 intocatalyst bed 6. After this radial flow, out to in, of gases, they arecollected in centerpipe 17 and immediately pass down and out to returnto catalyst bed 6, in radial flow, in to out, to finally pass intoannular gas collector 18. Gas is removed from zone 2 via line 18 andcharged to heater 61. Gas flow is maintained radially out to in, in theupper part of zone 2 and radially in to out in the lower part of zone 2by the strategic placing of imperforate baffles. The first bafflesencountered by entering gas are baffles 16 and 9 in outer annular space15. The path of least resistance for the gas is through catalyst bed 6into centerpipe 17. Once the gas enters centerpipe 17 it encountersanother obstacle, baffles 17 and 20 in the upper and lower portions ofthe centerpipe. The path of least resistance for the gas is againthrough catalyst bed 6 into annular space 18. Reactants are removed fromzone 2 via line 19. Baffles 30 and 31, in about the middle of zone 2'scatalyst bed, minimize short circuiting of gas from annular space 15 toannular space 18. If these baffles were merely a few centimeters thick,it would be much easier for gas to pass through the few centimeters ofcatalyst around the edge of the baffles, as opposed to passing throughthe bed of catalyst in radial flow. The baffles 30 and 31 may beslightly smaller than the baffles defining the upper or lower bounds ofa reaction zone. This is because adequate reaction of reactants willoccur as long as the reactants see catalyst, whereas re-heating of thereactants will not occur if the reactants do not go through aninterheater. Hence in this embodiment, wherein reheating was not needed,it was possible to minimize the size of baffles 30 and 31. As an addedbenefit of this design, the shortened baffle sections 30 and 31 alsopromote donward movement of catalyst in bed 5. Thus in the reactordesign of the present invention high reactant flow rates actuallypromote movement of the catalyst bed. Baffles 22 are longer than baffles30 & 31.

Reactants are heated in heater 61 and re-enter reactor 1 via line 23 toenter zone 3. Hot gases are distributed in outer annular space 24 andthen flow radially out to in through catalyst bed 6 into centerpipe 25.Gases are removed from centerpipe 25 via outlet 28. Baffles 21 and 27define the upper and lower limits of annular space 24. Baffle 20 andoutlet 28 define the limits of centerpipe 25.

Catalyst enters vessel 1 via catalyst inlets 50 shown at the top of thereactor. Multiple catalyst inlets 50 may be used and these multipleinlets may provide a reduction zone if needed for catalystpre-treatment. Alternatively, a reduction zone may be provided withinreactor vessel 1. The top of the catalyst bed 6 is sealed off from thereactor with upper cap 51. Upper cap 51 and baffle 12 define a stagnantzone through which little or no reactant flow occurs. This permitscatalyst to enter the reactor and be distributed uniformly withoutimmediately being subjected to contact with reactants. An analogousstagnant zone is provided at the lower end of catalyst bed 6 by lowercap 52 and baffle 26. Catalyst is withdrawn from vessel 1 via multiplecatalyst withdrawal lines 53.

In the embodiment shown in the drawing, reactant flow was generally downthrough the bed. This design was preferred because the sphericalreforming catalyst contemplated for use in this invention is freeflowing and very strong. In some instances, depending upon the height ofthe reactor and its width, and upon the strength and flowingcharacteristics of the catalyst, it may be desirable to modify thisscheme. Some catalysts tend to pack or bridge when subjected topressure. The reason for this is not completely understood at this time,but it is believed to be a phenomenon similar to that experienced whenworking with some sands when wet. When compressed, the sand will be afirm, rigid mass, yet when pressure is released, the sand reverts to afluid state. Thus, for some applications it may be desirable to minimizethe downward force of the catalyst, either because of flow or crushingconsiderations, by completely reversing the flow indicated.Alternatively, it may be desirable to reverse the flow of one or morebut less than all of the zones within a reactor.

Similarly, it may be desirable to provide for multiple reactant inletand outlet points, with symmetrical piping. This would promote uniformflow of gas. In the embodiment shown, this was not provided because theannular spaces provided were large enough, and the pressure drop acrossthe bed enough to promote uniform flow of gases entering each reactionzone.

Baffles may be provided on the inlet and outlet lines to at least splitthe flow into a clockwise and a counterclockwise component to minimizeproblems of poor reactant flow in any one part of the bed. It is alsobelieved slightly beneficial to provide offset inlets and outlets withina reaction zone, as indicated in reaction zone 2. Offsetting the inletsand outlets will tend to promote good fluid flow. Further, overworkingof catalyst on one side of the bed will be offset by overworking ofcatalyst on the opposite side, annularly speaking, of the catalyst bed,and catalyst which leaves the reactor should contain a relativelyuniform coke level. Thus, the reactor design of the present invention isvery forgiving of mistakes made in providing for good fluid flow throughthe catalyst bed.

As applied to a reforming embodiment, the reactor configuration for aunit processing 35000 BPSD (231.7 m³ /hr) of a naphtha charge stock isas follows. For a liquid hourly space velocity of 2.0, about 116 cubicmeters of catalyst is required in the active zone. Of course a certainaddition inventory of catalyst is required in the bottom of the catalystbed and at the very top to provide for sealing of the catalyst bed andfilling of the stagnant areas therein. This amount of catalyst is onlyabout 1 to 3 percent of the catalyst inventory. Of course a certainamount of catalyst inventory is required to be in a continuousregenerator, if one is used, or available for use as spent catalyst isaccumulated for periodic regenerations if a batch regenerator. Thereactor is designed to operate with a hydrogen to hydrocarbon mole ratioof 4, an inlet pressure to the first reaction zone of 12.5 atmospheres,absolute, and an outlet pressure from the last reactor of 11atmospheres. This is a very low pressure drop, and is indicative of theuse of low pressure drop heaters, and careful design of piping tominimize pressure drop. The relatively thin annular bed of catalyst,compared to prior art radial flow designs and especially compared toconventional fixed bed, down flow reactors, has a very low pressuredrop, but the tortuous path followed by the gas decreases somewhat theotherwise low pressure drop experienced in passing through a moving bedreactor of the present invention. The centerpipe diameter should be 1.2meters, and the diameter of the outer screen should be 2.4 meters. Thus,the catalyst bed is maintained as an annular bed with an inner diameterof 1.2 m and an outer diameter of 2.4 m. The reactor containmentvessel's inner diameter is 3.5 m. The low pressure drop experiencedthrough this catalyst bed was not believed sufficient to provide optimumgas distribution, so internal piping was provided in the second reactionzone to split the incoming gas flow into two streams, and the dischargepoints of these streams were placed 180° apart from one another. Each ofthese discharge points in turn split the flow into two directions, sothat gas entering and leaving the second reactor section did so via foursymmetrically spaced openings on both the inlet and outlet to zone 2.

To provide maximum heater efficiency, the screen separating zone 1 fromzone 2 was baffled over two meters of its length, or a little more thanthree times the thickness of the catalyst bed. This will insure thatover 90% of the gas leaving zone 1 will do so via the interheater. Thescreen baffle defining the upper and lower portions within zone 2 wasonly 1.2 meters thick, or twice the thickness of the catalyst bed. Thismeant that gas would have about as easy a path to take in flowinglaterally across the catalyst bed as down through the catalyst bed inthe section around this baffle point. This is not harmful, as it doesnot matter if the reactants contact catalyst in radial or downflow, aslong as contact occurs. The baffle separating zone 2 from zone 3 was twometers thick, again to insure that more than 90% of reactants leavingzone 2 will do so only via the interheater.

The height of catalysts in the very top of the reactor, immediatelyunder the catalyst addition lines, will be 0.5 meters. This height mustof course be coordinated with the number of catalyst addition points, inthis case, 16 symmetrically spaced pipes of 5 cm internal diameter.

The height of the zone 1 is 8 m, zone 2 is 10 m, and zone 3 is a 18.5 m.The total volume of catalyst will be 127 m³, which slightly exceeds the116 m³ required for a 2.0 LHSV. The difference is to allow for sealingof the top and bottom of the bed, and compensation for catalyst beingless exposed to reactants as it passes between the beds and for futureexpansion.

In the reforming embodiment, it is contemplated that the screens used tocontain the annular bed of catalyst will be free of obstructions andpromote smooth flow of catalyst. Screens which are especially wellsuited for this use are the well known Johnson well screens, originallydeveloped for use in water walls. These screens have triangular barswelded onto a support means. The catalyst sees a smooth, finished, flatsurface with a long spiral groove therein. Of course other types ofscreen, such as metal fabric, may also be used. The screen may alsoconsist of relatively thin walled pipe with many small holes or slotsdrilled or punched therein. The baffles may be metal plates welded orbolted onto the screens. If pipe with slots cut into it is used, theslots may be welded shut or simply omitted.

In the embodiment shown, the annular bed of catalyst maintains aconstant cross-sectional area from the very top of the bed to the bottomof the bed. This type of catalyst flow is preferred, because there is anabsolute minimum amount of shifting of catalyst which leads to abrasionand wear thereof. An acceptable variation, however, is to increase thecross-sectional area of the catalyst bed as it moves down the reactor.The increase in cross-sectional area should preferably occur betweenzones to simplify calculation of flow through each zone. The transitionfrom a thin to thicker bed may be made gradually or abruptly. Catalystcan easily flow into a larger space, but not so easily do the reverse.If the decision is made to increase the cross-sectional area of thecatalyst bed in the lower sections of the reactor, the amount of extrabaffling required on screening between reactor sections can easily bedetermined on the basis of the pouring characteristics of the catalystbeing considered. In the embodiment shown, if the third reactor sectionwere to be thicker than the preceding reactor sections, this could beaccomplished by keeping the centerpipe diameter constant and providingan outer screen of increased diameter. Increasing the outer screendiameter may be done by using a larger radius screen or by providingmultiple "scallops" ringing the inside of the wall of reactor 1 assubstitute for the outer screen. Thus, 50 or 60 semicircular verticalsections, similar to a pipe split in half, placed about the inside ofthe outer wall of reactor vessel 1, could define the outer limits of thecatalyst bed 6 in the third reaction section. Of course, if thecross-sectional area of the catalyst bed increased than the number ofcatalyst withdrawal points 53 should also be increased to provide foruniform withdrawal of catalyst from the bottom of the reactor bed.

The net effect of the present invention is to provide for a reactor andprocess wherein a moving bed of solids is given an easy and straightpath, while fluids which must contact the solid are given a moredifficult path to follow. Completely avoided is the necessity ofemptying the entire catalyst bed through a few narrow pipes andredistributing it to each lower catalyst bed. The "hour glass" passageof catalyst between beds, is eliminated. Simple gravity determines theflow of the catalyst, while fluid dynamics determines flow of fluid,resulting in much simplified piping for catalyst flow. Other benefitsinclude greater utilization of catalyst and a more compact reactordesign. Refiners also have a way to promote, or hinder, downflow ofcatalyst through a bed because of the unique flow characteristics of thepresent reactor design and process, which combines features of bothradial flow and up or down flow over a fixed bed of catalyst.

I claim as my invention:
 1. A process for hydrocarbon conversion of ahydrocarbon comprising contacting said hydrocarbons at hydrocarbonconversion conditions with a single vertical moving bed of catalystparticles disposed as a plurality of reaction zones which are verticallyspaced along the vertical length of the moving bed; said zones containedin an apparatus comprising a vertically elongated pressure tight vessel;a pair of vertical, concentric, inner and outer perforated screenspositioned intermediate the axis of said vessel and the outer wallthereof and defining an annular conduit filled with catalyst, saidconduit including a plurality of apertures at its upper and lower endsthrough which apertures active catlyst is added to the top of saidcatalyst bed and spent catalyst is removed from its bottom, saidapertures being connected to tubes which pass through the top and bottomof said vessel, a plurality of vertical, tubular inner and outer bafflemembers arranged in opposed relation at spaced locations along thelength of said conduit for preventing the radial flow of hydrocarbonthrough said catalyst bed; a plurality of inner and outer horizontalbaffle members affixed to at least some of said vertical baffle membersfor limiting the extent of axial flow of fluid through inner flowchambers defined by the hollow cylindrical space within said innerperforated screen and outer flow chambers defined by the hollow annularspace between said outer perforated screen and the outer wall of thevessel, said horizontal baffles and said vertical baffles cooperatingwith each other and with the wall of the vessel to divide said vesselinto a plurality of separate zones; fluid inlet and outlet means foreach of said zones passing through the walls of said vessel, the inletmeans for each of said zones being connected to one of the inner andouter flow chambers for the zone and the outlet means for each of saidzones being connected to one of the inner and outer flow chamber for thezone, whereby at least the major portion of fluid passing through eachzone will be forced to travel radially through the catalyst bed. 2.Process of claim 1 wherein the fluid is a naphtha, reforming conditionsand a reforming catalyst are used, and a reformate is recovered. 3.Process of claim 1 wherein the fluid is a paraffin, dehydrogenationconditions and a dehydrogenation catalyst are used and an olefin isrecovered.
 4. A process for the multiple reaction zone conversion of ahydrocarbon in a reactor vessel containing a single annular bed ofcatalyst comprising: a heating the hydrocarbon in a first temperatureadjustment means to hydrocarbon conversion temperature and charging thehydrocarbons into a first reaction zone by passing said hydrocarbonsradially through said catalyst bed; b removing hydrocarbons from thefirst reaction zone and charging it to an intermediate temperatureadjustment means; c removing hydrocarbon from the temperature adjustmentmeans and charging it to an intermediate reaction zone by passing thehydrocarbon into a first outer annular distributor around one-half ofthe vertical length of the intermediate reaction zone, interposingvertically disposed blocking media between the first outer annulardistributor and the below defined centerpipe and interposing ahorizontal blocking media in said below defined outer annulardistributor, passing hydrocarbon through the catalyst bed, in radial outto in flow, to a centerpipe defining the interior of the annular bed ofcatalyst within the intermediate reaction zone, and passing hydrocarbonsfrom said centerpipe through said bed of catalyst, in radial in to outflow, to a second outer annular distributor around the other one-half ofthe vertical length of the reaction zone; d withdrawing hydrocarbon fromthe intermediate reaction zone by withdrawing it from the seconddistributor and passing it to a final temperature adjustment means; eremoving hydrocarbon from the final temperature adjustment means andcharging it to a final reaction zone by passing hydrocarbons in radialflow through the catalyst bed; f withdrawing converted hydrocarbon fromsaid reactor vessel; and, g adding, at least periodically, activecatalyst to the top of the annular bed of catalyst and at leastperiodically withdrawing spent catalyst from the bottom of the annularbed of catalyst.
 5. Process of claim 4 wherein the annular bed ofcatalyst is defined by a perforate cylindrical screen which also definesthe inner distributor, and a perforate outer screen which also definesthe outer distributor.
 6. Process of claim 4 wherein said blocking mediaare defined by horizontal baffles in the inner and outer distributorsand vertical baffles on the inner and outer screens, whereby the majorportion of flowing hydrocarbon is forced to flow radially through thecatalyst bed in each reaction zone.
 7. Process of claim 4 wherein thevertical baffles have a height greater than the radial depth of thecatalyst bed.
 8. Process of claim 7 wherein the intermediate reactionzone is divided into two substantial equal sections, one for radial inflow and the other for radial out flow, defined by vertical baffles onthe inner and outer screens, at the top, middle and bottom and byhorizontal baffles in the outer distributor at the top, middle andbottom of the reaction zone.
 9. Process of claim 8 wherein the verticalbaffles at the top and bottom of each intermediate reaction zone have aheight greater than twice the radial thickness of the catalyst bed. 10.Process of claim 4 wherein the hydrocarbon is a petroleum naphtha, theprocess is catalytic reforming, and the temperature adjustment means areheaters.
 11. Process of claim 4 wherein the hydrocarbon is adehydrogenatable paraffin, the process is paraffin dehydrogenation, andthe temperature adjustment means are heaters.
 12. Process of claim 4wherein the first reaction zone is uppermost, the intermediate reactionzone is in the middle, and the final reaction zone is at the bottom ofthe reactor.
 13. Process of claim 8 wherein the intermediate reactionzone is divided into an upper and a lower section and gas flow throughthe upper section is radial in and gas flow through the lower section ofradial out.
 14. Process of claim 8 wherein the intermediate reactionzone is divided into an upper and a lower section and gas flow throughthe upper section is radial out and gas flow through the lower sectionis radial in.
 15. A process for altering the loading exerted by avertical moving annular bed of particles in a fluid stream whichcomprises: a containing in a pressure tight vessel a moving bed ofparticles in an annular bed between an inner perforate screen and anouter perforate screen; b providing two contiguous outer annulardistributors defined by the outer perforate screen, an inner wall of thepressure tight vessel, and a horizontal, imperforate baffle,intermediate the distributors; c providing an inner distributor definedby the inner perforate screen; d providing a vertical imperforatebaffle, with a vertical height less than three times the radialthickness of the particle bed, on the inner and outer perforate screensat the same level as the horizontal, imperforate baffle; and, emaintaining different fluid pressures in the outer distributors, therebycausing fluid to flow radially in from one outer distributor through theparticle bed to the inner distributor, and then to flow radially out tothe other outer distributor and also causing vertical flow of fluidthrough the bed of particulates whereby the vertical passage of fluidthrough the bed alters the loading exerted by the bed.
 16. Process ofclaim 14 wherein the loading of the particulate bed is decreased bycausing fluid pressure to be higher in the lower of the two outerannular distributors.
 17. Process of claim 14 wherein the loading of theparticulate bed is increased by causing fluid pressure to be higher inthe upper of the two outer annular distributors.